In general, the present invention relates to the field of communication systems. More specifically, the present invention relates to the generation of modulated radio frequency (xe2x80x9cRFxe2x80x9d) signals from a linear mixing of signals.
A direct-launch modulated signal source as known in the art includes a modulation signal source having a pair of digital-to-analog converter and low-pass filter combinations for providing both an in-phase baseband signal I and a quadrature baseband signal Q in analog form. The baseband signals I and Q are thereafter mixed with clock signals from a local oscillator, and then summed whereby the baseband signals I and Q are amplitude modulated and phase modulated. Since the baseband signals I and Q are in analog form, the mixers and a receiving power amplifier of the modulation signal source must be linear. This is a disadvantage of prior art direct-launch modulated signal sources, because linear power amplifiers are power inefficient.
A LINC modulated signal source as known in the art also includes a modulation signal source having a pair of digital-to-analog converter and low-pass filter combinations for providing the baseband signals I and Q in analog form. The prior art LINC modulated signal source provides the baseband signals I and Q to a pair of LINC synthesizers in order to generate two phase signals. A pair of phase modulators receive the phase signals, respectively, in order to generate two phase-modulated constant-envelope RF signals that must be amplified with high efficiency. The two RF signals are thereafter summed to obtain a desired amplitude modulated and phase modulated signal. The drawbacks of a prior art LINC modulated signal source is a complexity of the LINC synthesizers, a wide band requirement of the phase modulators, and a power efficient requirement of the signal combiner.
Thus, there is a need for a more efficient and less complex method to modulate a baseband signal containing amplitude- and/or phase-modulation to an RF frequency.
One form of the present invention is a modulated signal method. First, a baseband signal in digital form and a clock signal are received. Second, a pulse modulated signal in digital form is provided in response to a reception of the baseband signal and a reception of the clock signal, wherein the clock signal and the pulse modulated signal are synchronized.
A second form of the present invention is a modulated signal source comprising an oscillator and a pulse signal modulator. The oscillator is operable to provide a clock signal. The pulse signal modulator is operable to provide a pulse modulated signal in digital form in response to a reception of a baseband signal and the clock signal, wherein the clock signal and the pulse modulated signal are synchronized.